System and method for measuring grain cart weight

ABSTRACT

A system of improved weighing utilizes accelerometers to compensate for measurement dynamics and non-level sensor orientation. Fill level of remote combines can be estimated by utilizing their historical harvesting performance and elapsed time or area harvested. Failure and degradation of weight sensors is detected by testing sensor half bridges. Loading and unloading weights can be tied to specific vehicles by utilizing RF beacons. Display location diversity is enhanced utilizing a mirror located as necessary while reversing the displayed image.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation under 37 C.F.R. § 1.53(b) of U.S. patent application Ser. No. 15/526,731 filed May 12, 2017 now U.S. Pat. No. 10,760,946, the entire disclosure of which is hereby incorporated by reference, which is a National Phase entry under 35 U.S.C. § 371(c) of PCT Application No. PCT/CA2014/000810, filed Nov. 14, 2014, the entire disclosure of which is incorporated by reference herein.

BACKGROUND 1. Field of the Invention

The present invention relates to weighing dynamic loads and, more specifically, to apparatus and method for weighing grain cart loads.

2. The Prior Art

FIGS. 1A and 1B are drawings that show a combine 20 loading grain 22 from a field of grain 23 into a grain cart 10. FIG. 2 is a drawing showing a grain cart 10 with a grain truck 24. Grain carts 10 are large-capacity pull-type trailers with a container 12 for grain 22, a built-in discharge auger 18, and capacities currently as high as 2,000 bushels. A tractor 13 with grain cart 10 typically shuttles grain 22 from a combine 20 in a field to a grain truck 24 located at the edge of the field. The grain carts 10 are typically loaded by or from a combine 20, and then unloaded into a truck 24, with combines 20 and trucks 24 typically utilized with one or more grain carts 10 to harvest fields of grain. The use of grain carts dramatically increases harvest efficiency, allowing combines 20 to operate nearly continuously with no need to stop to unload, especially since grain carts 10 can be loaded from combines 20 while the combines and the grain cart they are loading move across the field together in a synchronized manner. While the grain cart 10 is away from the combine 20, the combine may continue to harvest the field, relying on its built-in hopper or grain container to buffer the harvested grain. After unloading to a waiting truck 24, the grain cart 10 can then head back to receive grain from a (not necessarily the same) combine 20.

Early adopters experimented with cart-based weighing systems, which quickly became standard equipment currently on roughly 80% of grain carts built in-factory. Weighing systems for grain carts allow the tracking of yields and help ensure that operators can accurately fill the truck to capacity with little risk of incurring fines for overweight loads. Grain carts make the use of combines more efficient; weighing systems can help make the whole process more efficient.

Grain cart weighing systems currently comprise two parts: weight sensors, and electronics that weigh the load and present information to the user—often called “indicators”. Currently, weight sensors are typically either load cells or weigh bars. Typically, a plurality of weight sensors is utilized for each cart. In one typical configuration, there is one weight sensor for each wheel and one for the tow bar or hitch. In another typical configuration, there is a plurality of weight sensors spread out around the grain cart container. Systems offered by market incumbents provide a monolithic measurement and display terminal typically situated in the tractor's cab with wires that connect back to the grain cart weight sensors, which may have been combined through a passive junction box. In their simplest form, standard weigh scale functions are provided including: zero; tare; and net/gross toggle. Advanced systems provide grain management functions allowing harvesting details to be captured as transactions.

However, while conventional methods and technologies have gained significant market acceptance, it has been noted that there are numerous issues with the current state of the art. Some of the recognized problems are as follows:

Measurement Dynamics.

While on-board weighing systems can generally provide accurate static measurements on level ground, weight measurements can be compromised by forces that originate either on-cart (auger operation) or from accelerations due to drops and impacts with obstacles on uneven terrain. The degree of measurement contamination relates to the specific terrain, cart resonances, and vehicle velocity—higher speeds having a more significant adverse impact on accuracy. FIG. 3 is a graph that illustrates the measurement dynamics that may be experienced while traversing a rough field, which contaminate the accuracy of the measured payload weight. This chart is an example of how measured weight can bounce around as a grain cart moves across a field. Weight sensors measure force, which relates to mass and any applied accelerations including that of gravity and those of vehicle dynamics encountered when a cart traverses uneven ground. When a bump results in an upward acceleration the weight sensors see an increased force, and when downward, a decreased force. This is true even if it were possible to maintain the alignment of the weight sensor toward the center of the earth. Even while stopped, uneven ground can result in inaccurate weight measurement, since the axis of sensitivity of the weighing sensor becomes misaligned with the gravity vector. This typically results in only a fraction of the load being measured by the weighing sensor, since the acceleration or force vector is no longer in just the direction of the axis of sensitivity of the weight sensor, but may include components in other directions.

Operations Tracking.

Lack of identification of the harvesting equipment (combine and truck) involved in grain transactions limits the usefulness of the collected management information. Although a grain cart operator could record such information manually, operator error due to the monotony and exhaustion suffered by cart operators leaves manually collected data unreliable.

No telemetric operational coordination currently exists between grain cart and combine. The efficiency of harvest operations could be increased through reception (or prediction) of combine fill-level and location for display to the grain cart operator.

Pre-Emptive Weigh Bridge Failure Detection.

Quality on-cart grain weighing is predicated on having functional weight sensors, such as weigh bars. Over time, these devices can fail by delamination of the internal strain gauges, vibrational stresses harming internal wiring, or by physical damage to the bar or external wiring. The damage can occur slowly or abruptly depending on the failure mode, but in all cases ultimately affects the weighing performance. The operator may misdiagnose slow or even the catastrophic failures and compensate for resulting measurement drifts or offsets by re-zeroing the scale indicator. Such remedies can result in weight inaccuracies and erroneous farm management data. If pre-emptively and properly diagnosed, defective sensors and wiring can be replaced before they impact production. However, there is no automated system or methodology available to detect and isolate this problem.

Display Location Diversity.

Although a scale display terminal is useful in both the loading (from combine) and unloading (to truck) phases, a single display cannot be positioned so that it may be viewed practically in both phases because the operator faces in opposing directions due to the relative locations of combine and truck during loading and unloading. Currently, either two displays are required, which is complicated and costly, or the operator must split his attention between the display and the grain transfer itself, which is error prone and inefficient.

What is needed, therefore, is a method or methods that can address the above identified problems in the current state of the art.

BRIEF SUMMARY OF THE INVENTION

This patent discloses and claims a useful, novel, and unobvious invention for improved weighing and related operational and data management functionality in the farm vehicle field.

According to a first aspect of the present invention, weight and simultaneous three-axis accelerometer measurements are used to compensate for at least some of the effect of non-level or rough terrain.

According to a second aspect of the present invention, a method automatically detects weights of grain transactions by differencing the weight signal as processed by two parallel low pass filters, each with different pass characteristics.

According to a third aspect of the present invention, a method of equipment usage tracking involves the use of beacons and signal strength detection as an indicator of proximity and therefore equipment identification.

According to a fourth aspect of the present invention, a method for estimating a combine's current fill level involves tracking combine performance using load weight per unit time and per unit area harvested.

According to a fifth aspect of the present invention, a method is presented for electrically testing weigh bars installed on a grain cart.

A detailed description of exemplary embodiments of the present invention is given in the following. It is to be understood, however, that the invention is not to be construed as being limited to these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are drawings that show a combine 20 loading grain 22 into a grain cart 10;

FIG. 2 is a drawing showing a grain cart 10 with a grain truck 24;

FIG. 3 is a graph that illustrates the measurement dynamics that may be experienced while traversing a rough field;

FIG. 4 is a drawing showing a grain cart 10 with weight sensors 14 installed, in accordance with an exemplary embodiment of the present invention;

FIG. 5 is a drawing similar to the drawing shown in FIG. 3, with a line fit to the data points utilizing least-squares;

FIG. 6A is a diagram that shows a standard weighbridge;

FIG. 6B is a diagram that shows diagnostic circuitry on a half bridge, in accordance with one embodiment of the present invention; and

FIGS. 7A and 7B are drawings that illustrate a tablet showing loading/unloading information. FIG. 7A shows the tablet normally, and FIG. 7B shows the tablet reversed.

DETAILED DESCRIPTION

The present invention differs from solutions offered by others as it does not have a monolithic topology, but instead uses a mobile device as the display terminal, user interface, and processing engine, and which connects wirelessly to electronics located on a grain cart. The signals from weight sensors are combined through use of a junction box; the resulting signal is then forwarded to the electronics for measurement, conversion, and transmission to the mobile device. Leveraging mobile devices in the present invention reduces product cost, increases processing capacity, and provides advanced data connectivity and navigational capabilities, while enhancing customer familiarity and thus market acceptance. This topology is shown in FIG. 4.

Exemplary embodiments of the present invention will now be described with reference to the appended drawings.

Measurement Dynamics.

Exemplary embodiments of the present invention can include techniques to assist with achieving improved weight and mass measurements as described below, using accelerometer-compensated mass measurement.

Effects of non-level orientation and in-motion vibration can be reduced from mass measurements by compensating weight measurements with simultaneous accelerometer measurements, given matching bandwidths. One exemplary embodiment uses STmicroelectronics LIS3DH three-axis accelerometer integrated circuits as part of a printed circuit board, with one three-axis accelerometer mounted preferably near each of the weight sensors.

FIG. 4 is a drawing showing a grain cart 10 with weight sensors 14 installed, in accordance with an exemplary embodiment of the present invention. The signals from each of the weight sensors are received by interface electronics with on-board three-axis accelerometer 16. The interface electronics 16 perform signal measurement, conversion, and transmission of the signals to a mobile device that may be located in the tractor 13 towing the grain cart 10. In one embodiment of the present invention, Bluetooth Low Energy (BLE) is utilized to transmit the signals wirelessly. Other transmission means are also within the scope of the present invention. In one embodiment of the present invention, the mobile device 17 receiving the signals is a tablet, such as an iPad. Other mobile devices 17 are also within the scope of the present invention. Moreover, while the device 17 typically utilized in the cab of the tractor 13 is mobile, it can also be permanently installed. Moreover, it can relay the information received, and the results of calculations and computations performed to other devices wirelessly or with a wired connection at a future time, for example, at the end of the work day.

Newton's law of motion is applied as follows in a preferred embodiment: F=m*a  (1) where “m” is the total mass of payload and carrier; “F” is the total instantaneous force of the payload and carrier weights as seen by the weight sensors; and “a” is the instantaneous acceleration projected along the axis of measurement of the weight sensors

Two exemplary methods are shown below sharing various commonalities. Common to both exemplary methods are sensor mounting, determination of reference gravity vector, and projection of the instantaneous acceleration measurements along the reference gravity vector.

Sensor Mounting:

Sensors are to be mounted as follows in the exemplary methods:

-   -   (1) Mount each single-axis weight sensor so that it is most         sensitive in the downward direction (toward the center of the         Earth) while the cart is stationary and on level ground. Other         configurations are also within the scope of the present         invention. However, this configuration is preferred, since it         easily allows a reference acceleration vector that aligns with         the axis of sensitivity of the weighing sensors to be recorded         when stopped on level ground.     -   (2) Mount one or more three-axis accelerometers in a convenient         orientation on the cart. In a preferred embodiment, one         accelerometer is mounted coincident with each weight sensor, and         a correction is preferably performed on the data from each         weight and accelerometer sensor pair. Other configurations are         also within the scope of the present invention.

Determination of Reference Gravity Vector:

Measure and record a vector of the static acceleration due to gravity while stationary and on level ground.

Projection of Accelerations Along the Axis of Measurement of the Weight Sensors:

Accelerations projected along the axis of measurement of the weight sensor(s) (a) can be determined by performing the scalar product (dot product) of the measured acceleration and the reference gravity vector, which aligns with the axis of measurement of the weight sensors due to the mounting method described above, and then dividing by the magnitude of the reference gravity vector.

In the first exemplary method, Equation 1 can be rearranged to yield mass as follows: m=F/a  (2)

The total force (F) is measured with respect to the weight offset (the measured value seen under free fall). The weight offset occurs at the point of zero acceleration, and represents offsets in the measurement apparatus including those of the weigh bars, amplifiers, and data converters. The total force (F) can thus be expanded to reflect the raw measured force (F_(MEAS)) and weight offset (k) as follows: m=(F _(MEAS) −k)/a  (3)

While it is impractical to measure the weight offset directly, a method is disclosed to find it as follows:

1) While traveling with constant mass over rough terrain, record weight (F_(MEAS)) and acceleration data pairs.

2) Compute the projections of the acceleration data on the axis of measurement of the weight sensors.

3) Estimate the weight offset (k) by computing the y-intercept of the least-squares line estimate of weight (F_(MEAS)) and projected accelerations (see FIG. 5).

FIG. 5 is a drawing similar to the drawing shown in FIG. 3, with a line fit to the data points utilizing least-squares. Once the weight offset (k) is known, the total mass (or weight under constant and known acceleration) can be determined by the following:

1) Measure the instantaneous weight (F_(MEAS)) and acceleration (a) data pair.

2) Compute the projection of the acceleration on the axis of measurement of the weight sensors.

3) Compute the total mass (m) using equation 3.

A second method requires no regression. Instead, two weight (F_(MEAS)) and acceleration (a) data pairs can be measured while traveling with constant mass, and the accelerations projected along the axis of measurement of the weight sensors (a). This provides two simultaneous equations and two unknowns based on Equation 3, thus allowing a solution for constant “k” using linear algebra techniques as follows: k=(F _(MEAS1) *a ₂ −F _(MEAS2) *a ₁)/(a ₂ −a ₁)  (4)

The weight offset (k) that is determined can be low-pass filtered over subsequent measurements to reduce the noise bandwidth. The filter's corner frequency can be set quite low, since “k” does not vary while mass is constant. The input data may be gated (manually or automatically) to ensure that the mass remains constant. Once the weight offset (k) has been determined to be sufficiently well characterized (it no longer changes significantly), the total mass (or weight under constant and known acceleration) can be determined using Equation 3.

With either exemplary method, the bandwidths of the weight and acceleration sensors should preferably be matched and the sampling time should be synchronized. In the exemplary embodiment, evaluation of the above equations is performed within a processor of the electronics in order to coordinate the measurements and reduce the needed radio bandwidth. The compensated measurements may then be forwarded to the mobile device in the tractor cab.

Automatic Operations Tracking.

Exemplary methods of the present invention may include techniques to aid in tracking and auditing field operations as described below.

Automatic Equipment Determination.

For the purpose of automating tracking and auditing, an exemplary method for automatically determining the particular equipment used in an operation is disclosed herein (for non-limiting example, a combine, truck, or trailer). According to this exemplary method, a wireless beacon device is placed on each piece of equipment, a receiver is located at or near the operator, and the system automatically selects from a list of allowed equipment types (for non-limiting example: combines or perhaps trucks) the equipment associated with the beacon of highest signal strength as the equipment used in an operation.

For a non-limiting example, while loading in the field, the combine currently loading the cart can be detected as closest and thus assigned to the transaction. Similarly, while unloading, a truck receiving the grain can be detected as the closest truck and thus assigned to the transaction. Combined with the time, location, and event details (for example transactional weight) a detailed audit trail can be provided for field operations.

In another non-limiting example, a list of detected equipment could be presented to the user and a selection by the user could be used to determine the equipment used in the operation. Before being presented to the user this list could be further limited to detected equipment where the associated beacon signal strength exceeds a threshold. This may be useful in cases where equipment is in close proximity such as when multiple trucks are waiting to be loaded with grain. In the case where only a single equipment has a beacon signal exceeding the threshold that equipment could be automatically determined as the equipment used in the operation.

The exemplary method uses stand-alone Bluetooth Low Energy (BLE) beacons, such as those currently available from Gelo Inc., mounted to each piece of equipment, and configured to periodically provide its identity. A mobile device mounted in the tractor cab monitors the announcements (e.g. Bluetooth “advertisements”) and processes the events in the manner disclosed in order to determine the nearest equipment. Other embodiments could include using an additional mobile device, acting as a beacon, mounted in the cab of the equipment being monitored (the truck or combine cab for non-limiting example). This is exemplary, and other configurations and implementations are also within the scope of the present invention.

Estimation of Combine Fill Level.

Another exemplary method is used to estimate the combine's current fill level while harvesting in order to facilitate operations in the field. By tracking the performance of each combine (load weight per unit time), the method can predict combine fill level using linear extrapolation as follows: {circumflex over (F)}(t)=ΣF _(LOAD) /Δt _(LOAD) *t  (5)

Where {circumflex over (F)} is the estimate of combine fill weight with time (t) since the last load; ΣF_(LOAD) is the accumulated weight of the N most recent loads; and Δt_(LOAD) is the time between the most recent load and the one preceding the N^(th) last load.

This exemplary method uses a value of one (1) for the window size (N). This exemplary method uses the processor of the mobile device to process weights of loads and the time between such in order that it estimate the combine's current fill level. Other configurations are also within the scope of the present invention. This estimate can be improved by instead using GPS locations services so that the system tracks combine performance per unit of field area harvested instead of per unit time. In this case, combine performance is rated as load weight per area harvested between loads. This method can predict combine fill level using linear extrapolation as follows: {circumflex over (F)}(a)=ΣF _(LOAD) /Δa _(LOAD) *a  (6)

Where {circumflex over (F)} is the estimate of combine fill weight with area harvested (a) since the last load; ΣF_(LOAD) is the accumulated weight of the N most recent loads; and Δa_(LOAD) is the area harvested between the most recent load and the one preceding the N^(th) last load.

This exemplary method uses a value of one (1) for the window size (N). This exemplary method computes the area harvested as the line-integral of the path traveled, multiplied by the harvester's header width, subtracting that portion of the swath that overlapped previously harvested swaths. The overlap is determined using a high-resolution grid representing the field whereby each harvested grid location gets marked so as to be excluded on subsequent paths. This exemplary method uses a grid size of one foot (1′) squared. Other configurations are also within the scope of this invention.

This exemplary method uses the processor of a mobile device in the tractor cab to process weights of loads as measured, along with the combine's current GPS location as measured and forwarded from a mobile device, mounted in the combine cab, over the wireless Internet cellular infrastructure. This is exemplary, and other configurations are also within the scope of the present invention.

In one embodiment the method further includes directing a grain cart to unload a first combine when the current fill level for the first combine exceeds a pre-specified threshold.

In another embodiment, the method further includes calculating an estimate of the current fill level for a second combine in the same manner as the estimate for the current fill level for the first combine was calculated; calculating a maximum estimated fill level from the estimated fill levels of each of a set of combines that comprise the first combine and the second combine; and directing a grain cart to a one of the set of combines corresponding to the maximum estimated fill level.

Although this method requires that information be shared between a combine and a cart, connectivity need not be continuous as the system can fall back to using time-based prediction during periods when the network is unavailable.

Automatic Weigh Bridge Health Detection.

Exemplary embodiments of the present invention may include a technique to electrically test the weigh bars or load cells while installed on the grain cart.

The technique performs operations to test all four resistors that form the standard weighbridge arrangement. The technique will also work where multiple weigh bars or load cells of a cart are wired in parallel (all like terminals wired together), so that the measured value for each weighbridge resistor approximates that of the parallel combination of all like resistors. This makes the measurement less sensitive by a factor of approximately the total number of weigh bars, and so measurement precision must be sufficient to reveal any anomalies.

FIG. 6A is a diagram that shows a standard weighbridge. FIG. 6B is a diagram that shows diagnostic circuitry on a half bridge, in accordance with one embodiment of the present invention. The analysis preferably splits the weighbridge symmetrically into left and right halves (see FIG. 6B). This is possible because the excitation connections are typically low impedance voltage sources (in the exemplary embodiment, positive and ground voltage rails).

In FIG. 6B, the voltmeter (circle with “V”) of the full bridge (FIG. 6A) has been decomposed into the buffer (BUF) and analog to digital converter (ADC) of the half bridge.

The analysis solves for the two half bridge resistors by measuring the voltage at the midpoint under various conditions and with different voltage references. The first step measures the ratio of the voltage divider formed by the two resistors while the current source is disabled. This is done using the excitation voltage (V_(CC) and Ground) as the reference for the ADC.

The next step uses a fixed voltage reference (often available internal to the ADC) and the ADC to measure the voltage at the midpoint of the half bridge while the current source is disconnected. This step is repeated with the current source connected.

Using network analysis techniques, the value of the top resistor can then be found as follows: R _(TOP)(V _(MID2) −V _(MID1))/(I*RATIO)  (7)

Where R_(TOP) is the resistance of the top resistor; V_(MID1) and V_(MID2) are the voltages measured at the midpoint of the half bridge with the switch open and closed respectively; I is the value of the constant current source; and RATIO is the measured ratio of the midpoint voltage with respect to the excitation voltage, with no current source.

Similarly, the value of the bottom resistor can be found as follows: R _(BOT)=(V _(MID2) −V _(MID1))/(I*(1−RATIO))  (8)

Where V_(MID1), V_(MID2), I, and RATIO are defined previously, and R_(BOT) is the resistance of the bottom resistor. In this exemplary embodiment, the processor of the electronics can perform the health measurements as directed by a mobile device in the tractor cab. Other configurations are also within the scope of the present invention.

Exemplary embodiments may also include a method to isolate individual weight sensors that have been combined as would be done through use of a junction box 15 (see FIG. 4), so that health detection can be performed on individual weight sensors in order to provide more thorough diagnostic capability. This embodiment involves replacing the passive junction box for which the like terminals of all weight sensors are permanently joined, with instead an active junction box whereby all connections for each weight sensor can be individually connected to (or disconnected from) the measurement electronics through use of digitally controlled switches, in order to present any possible combination of the weigh bars. In the exemplary embodiment, the measurement electronics control the switches of the active junction box. This is exemplary, and other configurations are also within the scope of the present invention.

This invention provides a number of different alternatives and embodiments. In one embodiment, the invention can be utilized to trouble shoot weight sensors that do not appear to be operating correctly. Pairs of resisters in the half bridges are serially tested, with note being taken whenever the results of the testing are problematic. In another embodiment, the weight sensors are tested on a routine or somewhat routine basis. For example, they may be tested on a periodic basis, or may be tested daily whenever the system is started. Other alternatives are also within the scope of the invention. A controller may send an alert when problems are discovered, or flags or codes set indicating problems. This allows weight sensors to be repaired or replaced before they fail or are inaccurate enough to affect operations. Other configurations and alternate usages are also within the scope of the present invention.

Enhanced Display Location Diversity.

Exemplary embodiments of the present invention may include a method to increase the diversity of display locations while in operation. A display is located for convenient viewing in one of the two grain transfer phases (loading or unloading). During the other phase, the operator views the display through a mirror positioned at an angle that is convenient for viewing during that phase; the mirror reflects an image that is deliberately reversed by the display equipment so that it becomes restored through reflection. Control of the reversing process could be applied automatically to reduce the burden on the equipment operator. For non-limiting example, reversing control could be linked to the automatic transaction detection method whereby the display is automatically reversed while unloading. In this case, the display would be mounted for convenient viewing during loading (combine to cart), and the mirror used while unloading (cart to truck). The opposite scenario would also be possible, whereby the mounting locations and reversing control are each reversed. Other configurations are also within the scope of the present invention.

FIG. 7A is a drawing that illustrates a tablet showing loading/unloading information. FIG. 7B is a drawing showing the same tablet shown in FIG. 7A, but reversed. The information shown in these displays is exemplary, and the display of other information and other configurations of the display are also within the scope of the present invention.

A user selectable element (not shown) such as a button or checkbox could be present in the user interface allowing the user to manually choose between the regular and reversed display. This may be useful for testing purposes, in the case the automatic detection fails to work, or simple user preference.

The device could also be configurable to disable one or more of the display reverse methods. For example, a user may desire to disable the automatic reverse because it is not useful in their work scenario. In another example, a user may desire to disable the user-selectable element because the automatic reverse meets their needs and they want more room on the display. This configurability could be present via an options or configuration menu in the user interface. Other configurations and options are also within the scope of the present invention.

The present invention is targeted at grain cart applications, but is equally applicable for use with other equipment, such as combines, trucks, planters, air seeders, and seed tenders. These types of equipment are exemplary, and other types are also within the scope of the present invention. In all cases, the invention can improve weighing performance, data quality, sensor diagnostics, and automates and enhances field operations.

Those skilled in the art will recognize that modifications and variations can be made without departing from the spirit of the invention. Therefore, it is intended that this invention encompass all such variations and modifications as fall within the scope of the appended claims. 

What is claimed is:
 1. A method of estimating combine fill levels on a computer system, the method comprising: calculating automatically, by a processor of the computer system, a total fill weight for a first combine by summing fill weights for all unloading operations for a specified metric; calculating automatically, by the processor, an estimate of fill rate by dividing the total fill weight by the specified metric; and calculating automatically, by the processor, an estimate of a current fill level for the first combine by multiplying the fill rate for the first combine by the specified metric since last unloading for the first combine, wherein the estimate of the current fill level improves the efficiency of a harvest operation.
 2. The method of claim 1, wherein: the specified metric is a one from a set consisting of area harvested by the first combine and time.
 3. The method of claim 1, further comprising: directing, by the processor, a grain cart to unload the first combine when the current fill level for the first combine exceeds a pre-specified threshold.
 4. The method of claim 1, further comprising: calculating, by the processor, an estimate of the current fill level for a second combine in the same manner as the estimate for the current fill level for the first combine was calculated; calculating, by the processor, a maximum estimated fill level from the estimated fill levels of each of a set of combines comprising the first combine and the second combine; and directing, by the processor, a grain cart to a one of the set of combines corresponding to the maximum estimated fill level.
 5. The method of claim 1, wherein: the specified metric is area harvested; and GPS location services are utilized to calculate combine performance per unit of field area harvested.
 6. The method of claim 5, further comprising: determining, by the processor, an overlap between a current swath harvested by the first combine and a previous swath harvested by the first combine; and calculating, by the processor, the area harvested by: determining a line-integral of a path traveled by the combine; multiplying the line-integral by the width of the header of the combine; and subtracting the overlap.
 7. The method of claim 6, wherein the determining the overlap further comprises: using, by the processor, a high-resolution grid representing a field; and marking, by the processor, each harvested grid location to be excluded from subsequent paths.
 8. The method of claim 7, wherein the size of each grid location is one foot squared.
 9. The method of claim 1, further comprising: displaying, by the processor, the current estimate of the fill level on a user interface of the computer system.
 10. The method of claim 1, wherein the computer system is a mobile device.
 11. A method for estimating combine fill levels on a first mobile device mounted in a tractor, the method comprising: calculating automatically, by a first processor coupled with the first mobile device, a total fill weight for a first combine; calculating automatically, by the first processor, an estimate of fill rate; calculating automatically, by the first processor, an estimate of a current fill level for the first combine; and directing a grain cart coupled with the tractor to unload the first combine when the current fill level for the first combine exceeds a pre-specified threshold.
 12. The method of claim 11, wherein: the calculating of the total fill weight for the first combine further comprises summing fill weights for all unloading operations for a specified metric; the calculating of the estimate of fill rate further comprises dividing the total fill weight by the specified metric; and the calculating of the estimate of the current fill level for the first combine further comprises multiplying the fill rate for the first combine by the specified metric since last unloading for the first combine.
 13. The method of claim 11, wherein: the specified metric is a one from a set consisting of area harvested by the first combine and time.
 14. The method of claim 11, further comprising: calculating, by the first processor, an estimate of the current fill level for a second combine in the same manner as the estimate for the current fill level for the first combine was calculated; calculating, by the first processor, a maximum estimated fill level from the estimated fill levels of each of a set of combines comprising the first combine and the second combine; and directing the grain cart to a one of the set of combines corresponding to the maximum estimated fill level.
 15. The method of claim 11, further comprising: determining, by a second processor of a second mobile device mounted in the first combine, a GPS location of the first combine, wherein the second mobile device is connected with the first mobile device via a network; forwarding, by the second processor, the GPS location of the first combine to the first processor; and calculating, by the first processor, a combine performance per unit of field area harvested using the GPS location of the first combine, wherein the specific metric is area harvested by the first combine.
 16. The method of claim 15, further comprising: switching, by the first processor, to using time as the specific metric when the connectivity between the first mobile device and the second mobile device is not available.
 17. A computer system for estimating combine fill levels, the computer system comprising: a processor coupled with the computer system, the processor configured to: calculate automatically a total fill weight for a first combine by summing fill weights for all unloading operations for a specified metric; calculate automatically an estimate of fill rate by dividing the total fill weight by the specified metric; calculate automatically an estimate of a current fill level for the first combine by multiplying the fill rate for the first combine by the specified metric since last unloading for the first combine; and direct a grain cart using the estimate of the current fill level for the first combine to improve the efficiency of a harvest operation by the grain cart.
 18. The computer system of claim 17, wherein: the specified metric is a one from a set consisting of area harvested by the first combine and time.
 19. The computer system of claim 17, wherein the processor is further configured to: direct a grain cart to unload the first combine when the current fill level for the first combine exceeds a pre-specified threshold.
 20. The computer system of claim 17, wherein the processor is further configured to: calculate an estimate of the current fill level for a second combine in the same manner as the estimate for the current fill level for the first combine was calculated; calculate a maximum estimated fill level from the estimated fill levels of each of a set of combines comprising the first combine and the second combine; and direct a grain cart to a one of the set of combines corresponding to the maximum estimated fill level.
 21. The computer system of claim 17, wherein: the specified metric is area harvested; and GPS location services are utilized to calculate combine performance per unit of field area harvested. 